Inhibition of the apical sodium-dependent bile acid transporter reduces LDL cholesterol and ApoB by enhanced plasma clearance of LDL ApoB

Objective-Cloning of the ileal apical sodium-dependent bile acid transporter (ASBT) has identified a new pharmacological target for the modulation of plasma lipoproteins. The objective of this study Was to determine whether a novel, specific, minimally absorbed ASBT inhibitor (SC-435) decreases LDL cholesterol through the alteration of plasma apoB kinetics. Methods and Results-Miniature pigs Were treated for 21 days with 10 mg/kg/day of SC-435 or placebo. SC-435 decreased plasma cholesterol by 9% and LDL cholesterol by 20% With no effect on other lipids. Autologous I-13-VLDL, I-125-LDL, and [H-3]-leucine were injected simultaneously to determine apoB kinetics. LDL apoB concentrations decreased significantly by 10% resulting entirely from an increase in LDL-apoB fractional catabolic rate. SC-435 had no effect on either total LDL apoB production or VLDL apoB converted to LDL. SC-435 increased VLDL apoB production by 22%; however, the concentration Was unchanged as a result of increased VLDL apoB direct removal. SC-435 increased hepatic mRNA and enzymatic activity for both cholesterol 7alpha-hydroxylase and HMG-COA reductase. Hepatic LDL receptor mRNA increased significantly, whereas apoB expression Was unaffected. Conclusions-A low dose of the ASBT inhibitor, SC-435, significantly reduces plasma LDL cholesterol through enhanced LDL receptor-mediated LDL apoB clearance, secondary to increased expression of cholesterol 7alpha-hydroxylase.